1. Field of the Invention
The present invention relates, in general, to fluorescent lamp devices. In particular, the invention relates to a compact type fluorescent lamp device having a plurality of straight arc bulbs closely disposed in parallel to one another. One end of each arc bulb is connected to another are bulb to form a relatively long crooked arc path.
2. Description of the Related Art
In recent years, the external shape of the arc bulb of a fluorescent lamp device has been changed to reduce the size thereof without decreasing the entire arc path thereof. In such a compact type fluorescent lamp device, the arc bulb thereof is formed in a H shape, a U shape, or a W-shape. One of the conventional compact type fluorescent lamp device is shown in FIGS. 1, 2 and 3. A pair of straight-shaped bulbs 11a and 11b of the fluorescent lamp device is extended in parallel to one another from a base 15. The extended end of each arc bulb 11a, 11b is communicated through a connecting tube 17. Thus, a substantially U-shaped arc path is formed in the pair of straight-shaped bulbs 11a and 11b and connecting tube 17 extended between straight-shaped bulbs pair 11a and 11b, as shown in FIG. 2. A stem 19a, 19b is provided to the other end of each straight-shaped bulb 11a, 11b. A pair of electrodes 21a and 21b is respectively disposed in each bulb 11a, 11b and is supported by stem 19a, 19b. A fluorescent material 23 is coated on the inner surface of each bulb 11a, 11b. A prescribed amount of a fill including mercury and a starting rare gas is sealed in bulbs 11a and 11b.
Base 15 includes a connector portion 25 and a pedestal portion 27, which are formed with an insulating material, e.g., synthetic resin. A first pair of base pins 29a is extended outward from connector portion 25. Both terminals of electrode 21a and first base pins pair 29a are electrically connected through a lead wire 31a, respectively. A second pair of base pins 29b also is extended outward from connector portion 25 Both terminals of electrode 21b and second base pins pair 29b also are electrically connected through a lead wire 31b, respectively. As shown in FIG. 2, the other end of each bulb 11a, 11b at which the pair of electrodes 21a and 21b is disposed is respectively inserted into pedestal portion 27 through a pair of holes 33a and 33b. The inserted end portion of each bulb 11a, 11b is supported such that a space between the inner surface of pedestal portion 27 and the circumferential surface of tho inserted end portion of each bulb 11a, 11b is filled with an elastic bonding agent 35, e.g., silicone.
In the above-described conventional fluorescent lamp device, diameters of the holes pair 33a and 33b are slightly greater than the external diameters of the bulbs pair 11a and 11b to easily insert the other end of each bulb 11a, 11b into the corresponding holes 33a and 33b. According to a design practice, it is designed such that the axis of each bulb 11a, 11b is coincident with the center of the corresponding holes 33a and 33b. Thus, a constant gap is maintained between the circumferential surface of each bulb 11a, 11b and the corresponding holes 33a and 33b in a radial direction. In other words, as shown in FIG. 3, an inner distance (a) is formed between the edge of hole 33a and the inner side surface of bulb 11a adjacent to bulb 11b, and an outer distance (c) also is formed between the edge of hole 33a and the outer side surface opposite to the above-described inner side surface of bulb 11a. In the same manner, an inner distance (b) is defined between the edge of hole 33b and the inner side surface of bulb 11b adjacent to bulb 11a, and an outer distance (d) is formed between the edge of hole 33a and the outer side surface opposite to the inner side surface of bulb 11b. Thus, each distance (a), (b), (c), (d) has the same dimension as one another.
In the above-described conventional compact type fluorescent lamp device, the output power of the lamp device was at most 36 watt (W) because of its compact external size. However, in recent years, a high output power fluorescent lamp device of the type, e.g., 55 watt (W), 96 watt (W), etc., has been developed. In the above-described low output power fluorescent lamp device, an entire length h of the arc bulb thereof, shown in FIG. 2, is about 410 (mm). However, in the high output power fluorescent lamp device described above, a distance between a pair of electrodes (an arc path) is more than 1000 (mm), and an entire length h is more than 560 (mm).
In the above described high output power fluorescent lamp device, cracks were observed in connecting tube 17, shown in FIGS. 1 and 2, during the operation of the lamp device. The inventor discovered cause of the cracks occurring in connecting tube 17 of the lamp such as a H-shaped fluorescent lamp device. When the H-shaped fluorescent lamp device shown in FIG. 2 is operated, arc tube 13 is heating and the temperature of the inner side surface of each bulb 11a, 11b facing to one another becomes greater than that of the outer side surface of each bulb 11a, 11b. This is because heat from the outer side surface of each bulb 11a. 11b is smoothly radiated. However, the inner Side surface of each bulb 11a, 11b is subject to a heat radiation from the inner side surface of the other bulb. Furthermore, an air convection scarcely occurs in a space defined by bulbs 11a and 11b adjacent to one the other. Thus, the inner side surface of each bulb 11a, 11b is expanded toward its opposite ends and the end portion of each bulb 11a, 11b in which electrodes 21a and 21b are respectively disposed is warped outwardly so as to move apart from one another, as indicated by an imaginary line m in FIG. 2. In addition, the temperature of the inner side surface of connecting tube 17 exposed to the space between bulbs 11a and 11b is higher than that of other surfaces thereof in a circumferential direction. For instance, when the H-shaped fluorescent lamp device of a 55 watt (W) rating was operated in a horizontal state at a room temperature of 25 degree centigrade (.degree.C.), the temperature of the inner side surface of bulb 11b at a point A shown in FIG. 2 was 90 degree centigrade (.degree.C.) and the temperature of the outer surface of bulb 11b at a point B was 70 degree centigrade (.degree.C.). Thus, it was observed that the distance between end portions of bulbs 11a and 11b was expanded to 3 to 5 (mm).
However, the mutual outward movement of the end portions of bulbs 11a and 11b is forcibly prevented by the corresponding edges of each hole 33a, 33b of base 15. Thus, connecting portion 17 receives a force caused by the expansion of the inner side surface of each bulb 11a, 11b. This results cracking of connecting portion 17.